267 lines
11 KiB
Python
267 lines
11 KiB
Python
# -*- coding: utf-8 -*-
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# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright (C) 2012 Yahoo! Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import abc
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import copy
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import functools
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import logging
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from taskflow.openstack.common import excutils
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from taskflow import exceptions as exc
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from taskflow import states
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LOG = logging.getLogger(__name__)
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class Flow(object):
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"""A set tasks that can be applied as one unit or rolled back as one
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unit using an ordered arrangements of said tasks where reversion is by
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default handled by reversing through the tasks applied."""
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__metaclass__ = abc.ABCMeta
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def __init__(self, name, tolerant=False, parents=None):
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# The tasks which have been applied will be collected here so that they
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# can be reverted in the correct order on failure.
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self._reversions = []
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self.name = name
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# If this chain can ignore individual task reversion failure then this
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# should be set to true, instead of the default value of false.
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self.tolerant = tolerant
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# If this flow has a parent flow/s which need to be reverted if
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# this flow fails then please include them here to allow this child
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# to call the parents...
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self.parents = parents
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# This should be a functor that returns whether a given task has
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# already ran by returning a pair of (has_result, result).
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#
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# NOTE(harlowja): This allows for resumption by skipping tasks which
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# have already occurred. The previous return value is needed due to
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# the contract we have with tasks that they will be given the value
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# they returned if reversion is triggered.
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self.result_fetcher = None
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# Any objects that want to listen when a wf/task starts/stops/completes
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# or errors should be registered here. This can be used to monitor
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# progress and record tasks finishing (so that it becomes possible to
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# store the result of a task in some persistent or semi-persistent
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# storage backend).
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self.task_listeners = []
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self.listeners = []
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# The state of this flow.
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self._state = states.PENDING
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# Tasks results are stored here...
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self.results = []
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@property
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def state(self):
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return self._state
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@abc.abstractmethod
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def add(self, task):
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"""Adds a given task to this flow."""
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raise NotImplementedError()
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def __str__(self):
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return "Flow: %s" % (self.name)
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@abc.abstractmethod
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def order(self):
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"""Returns the order in which the tasks should be ran
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as a iterable list."""
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raise NotImplementedError()
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def _fetch_task_inputs(self, task):
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"""Retrieves and additional kwargs inputs to provide to the task when
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said task is being applied."""
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return None
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def _perform_reconcilation(self, context, task, excp):
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# Attempt to reconcile the given exception that occured while applying
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# the given task and either reconcile said task and its associated
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# failure, so that the flow can continue or abort and perform
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# some type of undo of the tasks already completed.
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try:
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self._change_state(context, states.REVERTING)
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except Exception:
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LOG.exception("Dropping exception catched when"
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" changing state to reverting while performing"
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" reconcilation on a tasks exception.")
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cause = exc.TaskException(task, self, excp)
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with excutils.save_and_reraise_exception():
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try:
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self._on_task_error(context, task)
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except Exception:
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LOG.exception("Dropping exception catched when"
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" notifying about existing task"
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" exception.")
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# The default strategy will be to rollback all the contained
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# tasks by calling there reverting methods, and then calling
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# any parent flows rollbacks (and so-on).
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try:
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self.rollback(context, cause)
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finally:
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try:
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self._change_state(context, states.FAILURE)
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except Exception:
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LOG.exception("Dropping exception catched when"
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" changing state to failure while performing"
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" reconcilation on a tasks exception.")
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def run(self, context, *args, **kwargs):
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if self.state != states.PENDING:
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raise exc.InvalidStateException("Unable to run flow when "
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"in state %s" % (self.state))
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if self.result_fetcher:
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result_fetcher = functools.partial(self.result_fetcher, context)
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else:
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result_fetcher = None
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self._change_state(context, states.STARTED)
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task_order = self.order()
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last_task = 0
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was_interrupted = False
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if result_fetcher:
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self._change_state(context, states.RESUMING)
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for (i, task) in enumerate(task_order):
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if self.state == states.INTERRUPTED:
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was_interrupted = True
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break
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(has_result, result) = result_fetcher(self, task)
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if not has_result:
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break
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# Fake running the task so that we trigger the same
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# notifications and state changes (and rollback that would
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# have happened in a normal flow).
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last_task = i + 1
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try:
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self._on_task_start(context, task)
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# Keep a pristine copy of the result
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# so that if said result is altered by other further
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# states the one here will not be. This ensures that
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# if rollback occurs that the task gets exactly the
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# result it returned and not a modified one.
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self.results.append((task, copy.deepcopy(result)))
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self._on_task_finish(context, task, result)
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except Exception as e:
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self._perform_reconcilation(context, task, e)
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if was_interrupted:
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return
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self._change_state(context, states.RUNNING)
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for task in task_order[last_task:]:
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if self.state == states.INTERRUPTED:
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was_interrupted = True
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break
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try:
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has_result = False
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result = None
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if result_fetcher:
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(has_result, result) = result_fetcher(self, task)
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self._on_task_start(context, task)
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if not has_result:
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inputs = self._fetch_task_inputs(task)
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if inputs is None:
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inputs = {}
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inputs.update(kwargs)
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result = task.apply(context, *args, **inputs)
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# Keep a pristine copy of the result
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# so that if said result is altered by other further states
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# the one here will not be. This ensures that if rollback
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# occurs that the task gets exactly the result it returned
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# and not a modified one.
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self.results.append((task, copy.deepcopy(result)))
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self._on_task_finish(context, task, result)
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except Exception as e:
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self._perform_reconcilation(context, task, e)
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if not was_interrupted:
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# Only gets here if everything went successfully.
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self._change_state(context, states.SUCCESS)
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def reset(self):
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self._state = states.PENDING
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self.results = []
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self._reversions = []
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def interrupt(self):
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self._change_state(None, states.INTERRUPTED)
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def _change_state(self, context, new_state):
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if self.state != new_state:
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old_state = self.state
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self._state = new_state
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self._on_flow_state_change(context, old_state)
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def _on_flow_state_change(self, context, old_state):
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# Notify any listeners that the internal state has changed.
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for f in self.listeners:
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f(context, self, old_state)
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def _on_task_error(self, context, task):
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# Notify any listeners that the task has errored.
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for f in self.task_listeners:
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f(context, states.FAILURE, self, task)
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def _on_task_start(self, context, task):
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# Notify any listeners that we are about to start the given task.
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for f in self.task_listeners:
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f(context, states.STARTED, self, task)
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def _on_task_finish(self, context, task, result):
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# Notify any listeners that we are finishing the given task.
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self._reversions.append((task, result))
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for f in self.task_listeners:
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f(context, states.SUCCESS, self, task, result=result)
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def rollback(self, context, cause):
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# Performs basic task by task rollback by going through the reverse
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# order that tasks have finished and asking said task to undo whatever
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# it has done. If this flow has any parent flows then they will
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# also be called to rollback any tasks said parents contain.
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#
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# Note(harlowja): if a flow can more simply revert a whole set of
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# tasks via a simpler command then it can override this method to
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# accomplish that.
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#
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# For example, if each task was creating a file in a directory, then
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# it's easier to just remove the directory than to ask each task to
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# delete its file individually.
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for (i, (task, result)) in enumerate(reversed(self._reversions)):
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try:
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task.revert(context, result, cause)
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except Exception:
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# Ex: WARN: Failed rolling back stage 1 (validate_request) of
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# chain validation due to Y exception.
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log_f = LOG.warn
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if not self.tolerant:
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log_f = LOG.exception
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msg = ("Failed rolling back stage %(index)s (%(task)s)"
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" of flow %(flow)s, due to inner exception.")
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log_f(msg % {'index': (i + 1), 'task': task, 'flow': self})
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if not self.tolerant:
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# NOTE(harlowja): LOG a msg AND re-raise the exception if
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# the chain does not tolerate exceptions happening in the
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# rollback method.
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raise
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if self.parents:
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# Rollback any parents flows if they exist...
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for p in self.parents:
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p.rollback(context, cause)
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